1. Field of the Invention
The present invention relates to internal combustion engines, particularly to two-stroke engines, and specifically to an apparatus and method using control slide members to regulate flow through exhaust ports in the cylinders of such engines
2. Background Art
The two-stroke engine involved as background to the present disclosure is a spark ignition internal combustion engine as may be employed, for example, to power a motorcycle or an all-terrain vehicle (ATV) in which scavenging the cylinder occurs via ports provided in the cylinder wall and controlled by the piston.
Such an engine can feature a plurality of scavenging passageways via which a mixture of fuel and air gains access to the combustion chamber of the cylinder, and at least one exhaust passageway via which the exhaust gas can be scavenged from the combustion chamber.
To achieve a high power output by minimizing the flow resistances detrimental to scavenging the exhaust gas, the exhaust port needs to be dimensioned large. Dimensioning the exhaust port large, however, incurs the risk that a piston ring provided on the piston of the engine may get entrapped at the top or bottom metering edge of the exhaust port, resulting in damage to the cylinder bore, or piston ring and the piston respectively. To avoid this problem, the exhaust port can feature a web which helps in preventing the piston ring from becoming entrapped at the edges of the exhaust port due to its guidance of the piston ring. Such a web poses, however, a resistance to flow and, apart from this, is a drawback technically in production.
This is why it is also already known to provide, in addition to the main exhaust port located usually in the direction of travel of the vehicle powered by the engine, auxiliary exhaust ports angularly spaced away from the main exhaust port so that the latter can be configured correspondingly smaller. The smaller configuration lessens the tendency for the piston ring to get entrapped, and nevertheless still makes available in sum larger flow cross-sections for scavenging the combustioned exhaust gas from the combustion chamber.
To improve the performance of such a two-stroke engine by attempting to achieve an ideal type displacement scavenging, without scavenging losses of the new fresh gas, it is known to provide exhaust port control members which cover at least partially the exhaust port of the engine while in the low engine speed RPM range. Such control member use attains by altering the timing of the engine better charging of the cylinder, and thus improving the power and torque response of the engine in the low engine speed RPM range. Such benefits are realized whilst achieving a more ample torque characteristic along the engine speed curve, due to the ability to change the exhaust timing as a function of the engine speed.
For this purpose control slides have already become known, including plate-shaped to cover at least partially the main exhaust port of the engine, and so-called rotary slides configured roller- or barrel-shaped. Rotary slides are used to control the auxiliary exhaust ports of the engine by a rotating motion about their native axis of rotation produced, for example, by means of electric powered servomotors. Unfortunately, a two-stroke engine having such an exhaust control arrangement is complicated in design and accordingly also expensive to manufacture.
To attain a more ample torque curve and high peak power also in the medium and higher RPM speed range of a two-stroke engine provided with such an exhaust control, the control slide members provided in the main and auxiliary exhaust ports are, for example, controllably uncovered to achieve, via a corresponding resonance design of the exhaust portion and in uncovering the exhaust ports, the wanted characteristic whilst nevertheless attaining a more ample increase in the torque curve in the low RPM speed range.
Known already from DE 195 35 069 A1 is a two-stroke engine featuring a curved control slide member to reduce the dead space between the curved cylinder wall and the control slide in the exhaust system because dead space is a disadvantage to the power and torque response of the two-stroke engine. This known two-stroke engine features only one main exhaust port, however.
Known from U.S. Pat. No. 5,752,476 A if a two-stroke engine featuring a control slide member for the main exhaust port and rotary slide members for the auxiliary exhaust ports as already explained above.
Known from AT 005 299 U1 is a two-stroke engine featuring an actuator pressurized by the exhaust gas of the engine, the actuator being arranged in the region of the cylinder of the engine. However, including such a known two-stroke engine in a frame of a known motorcycle would result in the actuator getting in the way of a leading or bracing tube down swept from the steering head tube of the frame towards the road surface.
Known from U.S. Pat. No. 6,244,227 B1 is a valve assembly for exhaust port control of a two-stroke engine actuated by an actuator pressurized by a gas from a pressurized gas source provided for this purpose.
Known from CA 2 355 038 A1 is a two-stroke engine featuring main and auxiliary exhaust ports, each of which can also be uncovered and covered at least partially by separate control slide members. For this purpose a yoke is provided actuated by a gas pressurized actuator to overcome the force of a spring, the main and the two auxiliary exhaust port members being secured to the yoke to actuate first the auxiliary exhaust port members and then the main auxiliary exhaust port member, each independent of the other. In other words, the known control slide member assembly comprises three separate control slide members which thus require three grooves or recesses machined in the cylinder for the control slide members, each configured separately from the other. This necessitates wall and guiding portions in the recesses of the cylinder for guiding the individual control slide members which makes for a complicated and costly production. In addition to this, a plurality of different control slide members needs to be produced, each different from the other and which then need to be assembled in manufacturing the engine.
With the foregoing as background, the present invention was developed and dedicated to eliminating the drawbacks explained hereinabove. The disclosure includes and apparatus and method for defining a two-stroke internal combustion engine comprising, in addition to a main exhaust port, also auxiliary exhaust ports which can be covered at least partially by control slide members, and an innovative control slide provided therefore to greatly simplify manufacture with less complicated production for accommodating the control slide in the cylinder.